1. Field of the Invention
This invention relates generally to an apparatus and method for non-destructive, guided inspection of an object. More particularly, the invention is directed towards ultrasonic inspection of internal structural features using eddy current probes to guide the ultrasonic inspection.
2. Background Information and Description of the Prior Art
This invention relates generally to non-destructive examination of internal structural components of an object. The device is specifically directed towards an apparatus and method for inspecting internal components using ultrasound inspection techniques which are guided by eddy current probes. The eddy current probes detect the location of the internal structure such that the ultrasonic energy will be appropriately directed and the resulting data will be accurately interpreted. The invention is particularly useful for inspection of internal ribs in an aircraft wing or weld seams in piping or welded components of a structure.
Devices for inspecting objects in a non-destructive manner using ultrasonic inspection probes, or eddy current inspection probes have been known. One device and method which discloses the use of a combination of ultrasonic and eddy current probes for inspection of a device is owned by the assignee of the present invention. More specifically, U.S. Pat. No. 4,856,337 discloses an apparatus and method for providing a combined ultrasonic and eddy current inspection of a tube. The device is directed towards inspecting the walls of conduits such as heat exchanger tubes in nuclear steam generators. The eddy current probe is used to inspect the surfaces of the metal walls of the tube and the ultrasonic probe is used to check for internal flaws in the tube walls. A drive train is provided to impart a helical motion to a probe carrier which travels throughout the tube to be inspected.
Another apparatus which discloses use of both ultrasound and eddy current inspection probes is disclosed in U.S. Pat. No. 4,167,878. The device utilizes ultrasonic probes to test for internal flaws and an eddy current device to test for surface flaws. The device is arranged such that the two testing probes have at least approximately a common central axis.
Other devices for inspecting objects for subsurface flaws utilizing sonic transducers have been known, such as the device disclosed in U.S. Pat. No. 4,559,825.
One of the problems which arises in non-destructive industrial testing is that of precisely locating a flaw which has been detected by an ultrasonic transducer device. Typically, an indication that a flaw exists is generated by the ultrasonic transducer but the difficulty arises in detecting the exact location of the defect with respect to the internal structure. U.S. Pat. No. 4,235,112 discloses a laterally movable ultrasound transducer for use in inspecting rail faults. The device includes a pair of ultrasound receiving transducers positioned on either side of a main transmitting transducer. Signals provided by the receiving transducers are compared and the signals are used to determine and control the lateral position of the sensor with respect to the rail being inspected. Another method for determining the position of a measuring sensor or probe was disclosed in U.S. Pat. No. 4,530,243. This method primarily focuses on determining position with respect to a frame by measuring voltage drops across individual bars comprising the frame to determine the relative position of a detected flaw with respect to the bars of the frame.
An ultrasonic inspection system including apparatus and method for tracking and recording a location of an inspection probe was disclosed in U.S. Pat. No. 4,160,386. This device and method includes one or more sources of radiant energy located on a probe which are periodically actuated as the probe is moved about an object being inspected. The radiant energy is detected by receiving devices or microphones located at known points with respect to the area being inspected or with respect to a known reference point such as a weld. As the radiant energy is picked up by the receiving devices, the location of the probe can be determined and recorded.
The above mentioned devices provide apparatus and methods for non-destructive industrial testing utilizing ultrasound and, in some cases, combinations of ultrasound and eddy current devices. As discussed, some methods are also disclosed for locating the position of the probe with respect to a known point to provide a method for determining the location of a detected flaw with reference to that known point. However, these methods are not entirely reliable and, in addition, these devices have not heretofore provided a method for determining where to direct the ultrasonic energy for the inspection. More particularly, it is often necessary to focus the inspection upon a particular internal structural member of an object which is known to be prone to developing cracks, tears or other structural defects. However, if such internal structural components are not visible, there is difficulty in determining where to direct the ultrasonic energy in the course of an inspection. For example, inspection of aircraft wings has become of increasing importance in both commercial and military aviation with respect to aging aircraft. Inspection of the wings is directed primarily towards inspection of the underlying ribs or T-shaped cross sections which provide the structure for the airfoil. This rib is often called a stringer. The area where the stringer joins the surface of the airfoil is often a high stress region and a non-destructive examination of this region is typically included in routine service inspection requirements. It is important to direct an ultrasonic inspection at this region of the wing.
A typical wing panel inspection would first involve locating the ribs or stringers. Conventionally, a special template is placed on the wing surface and the rib location is marked. The template is used along with engineering drawings of the wing to determine the exact location of the ribs. A manual ultrasonic inspection would then be conducted during which the transducer is moved back and forth across the rib region. Although the test is simple in principle, the use of the rib-locating template is very time consuming. In addition, interpretation of test results can be extremely difficult and can be inaccurate because the aircraft wings are often not built in exact conformity with the original engineering drawings. Data interpretation problems also stem from the fact that a crack signal can be masked by a top plate thickness signal. Thus, positioning of the transducer at the rib is critical to developing accurate, reliable data.
Similarly, problems arise in inspecting for cracks and tears along a weld seam in piping or other ducts and conduits. Of particular interest are components which have had the weld crown machined so that it is flush with the base metal as is often the case with welded pipe. To inspect the weld metal and adjacent heat-affected zone, a manual ultrasonic angle beam examination is routinely performed. To assure that the complete weld zone is inspected, the weld region and designated inspection area is outlined in a grid pattern with a marker pen on the surface of the component. However, initially identifying the actual weld location after the crown has been removed is difficult and often requires expensive and time consuming metal etching procedures before the inspection can take place.
There remains a need, therefore, for a device which can be incorporated with ultrasonic inspection probes, and which can provide guidance for the probe to a desired location on an object such that the ultrasonic energy can be directed towards a pre-selected internal structure to be inspected. In addition, there remains a need for a device which can be used to eliminate false discontinuity signals which are generated from internal structures from actual discontinuities representative of internal flaws in the object.